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From:Jim Faucette Date:June 22 1999 9:55pm
Subject:Re: Update,Insert and Select
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If I remember correctly, Monty recently suggesting grouping UPDATES and
INSERTS whenever possible. It should improve IO performance.

  jim...

Sasha Pachev wrote:
> 
> Dan Nelson wrote:
> >
> > In the last episode (Jun 22), David Johnson said:
> > > Sasha Pachev <sasha@stripped> said:
> > > > I have noticed that unlike selects, updates and inserts are more
> > > > disk I/O than CPU bound. Setting key_buffer to 0 in this situation
> > > > actually improved performance. Regardless of the buffer settings,
> > > > disk I/O is very intensive and mysqld is using only a very small
> > > > fraction of CPU.
> > > >
> > > > Does that mean that if someone is doing a lot of inserts and
> > > > updates they need to focus on a fast disk? Or maybe there is a way
> > > > to tweak the settings to avoid it (other than mounting ramdisk on
> > > > /usr/local/mysql/data/db_name) What do you guys think?
> > >
> > > We are quickly running into the IO boundary problem.  We do allot of
> > > updates and have recently figured out that we will run into the IO
> > > wall long before we run into the CPU wall.
> > >
> > > We would be VERY interested in avoiding that problem.
> >
> > You're pretty much stuck with it, I'm afraid.  Inserts and updates have
> > to modify both the table and any affected indexes, and have to sync the
> > data to avoid corruption in case of a crash.  You can make selects
> > faster by adding RAM (and caching more of your table/indexes), but more
> > RAM doesn't help updates much at all.
> >
> > Bigger databases (like Oracle) overcome this problem by using redo logs
> > and background database writer processes to optimize writes, and by
> > using row or block-level locking so that multiple updates can happen
> > simultaneously.
> >
> > Mysql doesn't have either redo logs or fine-grained locking, so you'll
> > just have to buy the fastest disks you can find, and/or get a
> > nonvolatile disk cache like Prestoserve.
> >
> 
> I have done some more benchmarks and discovered that creating a
> reasonable amount of smaller tables can speed up inserts and updates. In
> my case:
> 
> one large table with 1 million records - about 70 updates/s
> the same table broken down into 64 smaller tables - worst case - 190
> updates/s, sometimes 520 updates/s.
> 
> One way to improve the smaller table performance would be to schedule
> the queries better, queue up several sorting them according to which
> table they will be modifying, and then once in a while flushing the
> queue. The advantage of this is that you can do lock tables, and also
> this will cause less disk swapping since the update will be more
> orderly.
> --
> Sasha Pachev
> http://www.sashanet.com/ (home)
> http://www.direct1.com/ (work)
> 
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Thread
Update,Insert and SelectSasha Pachev23 Jun
  • Re: Update,Insert and SelectDavid Johnson23 Jun
    • Re: Update,Insert and SelectDan Nelson23 Jun
  • Re: Update,Insert and SelectSasha Pachev23 Jun
  • Re: Update,Insert and SelectJim Faucette23 Jun
  • Update,Insert and SelectMichael Widenius29 Jun